1. Field of the Invention
This invention relates to thermal inspection of electrical equipment using an infrared camera, and in particular to an infrared sight glass adapted for rapid fitment to an existing enclosure without needing access to the interior of the enclosure containing the monitored equipment.
2. Description of Related Art
Thermographic inspection of electrical equipment is carried out using a specially adapted camera which registers infrared radiation and converts this to a visible image. The particular advantage is that for accurate thermographic inspections to take place, the equipment to be inspected must be under normal running conditions. A problem occurs when the electrical equipment is contained within an enclosure, and the infrared radiation which the camera detects is unable to penetrate the enclosure in an identifiable form. The provision of a glass or plastic sight glass in the equipment would not solve the problem as infrared radiation cannot penetrate either of these mediums. The solution is to use a sight glass which contains an infrared transparent medium. Infrared transparent sight glasses in the prior art suffer from the following disadvantages: 1) They require access to the interior of the enclosure to facilitate installation, and 2) The fragile infrared transparent medium is protected by means of a rotating shield or cover which when closed is not locked into place, thus such a sight glass cannot be used in public places where unauthorized persons could be exposed to an electric shock hazard.
In U.S. Pat. No. 5,793,522, issued Aug. 11, 1998 to Michel Brun, of Bizanos, France and assigned to Comet, of Paris, France discloses an observation window for checking the temperature of objects within a screened cabinet using infrared thermographics. An observation window comprising a parallel-faced transparent insert is provided which is made of a single crystal suitable for radiation to pass through without being substantially changed, such radiation having a wavelength, which may range from the visible to the relatively far infrared, emanates from an object whose temperature is to be monitored. The insert is fitted into a support which surrounds it at its periphery with respect to the support. The support is applied in a sealed manner against an aperture in the door and then locked in position by means that are only accessible from inside the cabinet.
Therefore, it is desirable to have an infrared sight glass that may be installed on the enclosure of operating electrical equipment from the outside without the need for access to the inside of the enclosure.